The present invention relates to a control method of a gas turbine and, more particularly to a control method of a gas turbine which is provided with two stage type combustors each having a first stage combustion part effecting diffusion combustion and a second stage combustion part effecting premixed combustion.
Each combustor of the gas turbine which is provided with a plurality of two stage type combustors and generally used has a first stage combustion part in which diffusion combustion is effected and a second stage combustion part in which premixed combustion is effected, as disclosed in JP A 7-63334. One of features of the two stage type combustors of this kind of a gas turbine is that a fuel air ratio or a ratio between a fuel quantity and an air quantity changes very widely from starting to a rated load operation.
The gas turbine having two stage type combustors is possible to achieve low NOx combustion even in this very wide range of change in fuel air ratio, and the low NOx combustion is achieved by combustion control of the first stage combustion part and the second stage combustion part. That is, in the first stage combustion part which is used from start-up to a prescribed low load, diffusion combustion which has a wide operation range is used, and then the combustion is shifted from independent combustion in the above-mentioned first stage combustion part to simultaneous combustion in the first stage combustion part and in the second stage combustion part effecting premixed combustion in order to effect low NOx combustion even in a high load region, or individual combustion in the second stage combustion part in order to realize further low NOx combustion.
However, combustion subtly changes according to difference between combustor individuals, change in temperature or humidity of the combustion air or change in calorific amount and composition of the fuel. Particularly, in the case where the gas turbine is provided with a plurality of the combustors, since the combustion conditions of the respective combustors are different from each other, stable combustion is required further.
On the other hand, the NOx concentration changes sensitively to a fuel air ratio, and since a stable combustion range is narrow, fine control of the fuel air ratio is necessary.
Therefore, for the combustion condition of the second stage combustion part which is a premixed combustion part, it is necessary to finely control a quantity of fuel and a quantity of air within the narrow stable combustion range in order to lower the above-mentioned NOx concentration, while the combustion condition has a tendency for becoming very unstable because of influence of difference in combustor individuals, etc.
For this reason, even if secondary fuel which is fuel for the second stage combustion part is injected into the second stage combustion part, there was such possibility that firing from the first stage combustion part to the second stage combustion part could not be effected, so that the secondary fuel could not be ignited or was misfired in the second stage combustion part, or on the contrary, such possibility that the fuel quantity injected became a little more than the quantity corresponding to the air quantity, so that the corresponding portions were damaged by burning with the flame being approached.
As conventional technique, there is a control method of continuously operating a gas turbine as shown in JP A 7-63334, in which as for abnormal combustion condition in a second stage combustion part, a quantity of state representative of the combustion condition of above-mentioned combustor or gas turbine is monitored, when it exceeds an allowable value and the combustion condition is regarded as an abnormal combustion, a load of the gas turbine is lowered at a stroke to a low load of individual combustion operation in the first stage combustion part for diffusion combustion which is stable in combustion, whereby the gas turbine is continuously operated.
A first object of the present invention is to provide a control method of a gas turbine having a two-stage type combustor effecting diffusion combustion and premixed combustion, which method enables the gas turbine to avoid lowering in load to a low load region and to extremely suppress a decrease of power generation by continuously operating the gas turbine in a prescribed low load region in a use region of the premixed combustion part when an abnormal combustion occurs in the combustor.
Further, a second object of the present invention is to provide a control method of a gas turbine having a two-stage type combustor effecting diffusion combustion and premixed combustion, which method enables the gas turbine to avoid lowering in load to a low load region by continuously operating the gas turbine in a prescribed low load region in a use region of the premixed combustion part when an abnormal combustion occurs in the combustor, and to reduce a time period until the plant is restored to a prescribed rated load by monitoring a quantity of state representative of combustion condition of the above-mentioned combustor or gas turbine and rapidly restoring to an original operation condition.
The present invention made a control method of a gas turbine having a plurality of combustors each of which has a first stage combustion part effecting diffusion combustion and a second stage combustion part effecting premixed combustion to attain the effected object by monitoring a quantity of state representative of combustion condition of the above-mentioned combustor or gas turbine, and regarding the combustion condition as abnormal combustion and lowering the gas turbine load to a prescribed partial load when the quantity of state exceeds an allowable value, thereby to continuously operate it.
Further, during control of the gas turbine in which the combustion is regarded as being abnormal and the load is lowered as mentioned above, the control is effected so that an opening of air compressor inlet guide vanes is kept as it is or reduced to decrease, whereby a fuel air ratio is lowered and the possibility that apparatus and devices are damaged is reduced.
Further, the present invention is so made that the above-mentioned quantity of state is taken by at least one of combustion gas temperature or metal temperature of the combustor or piping around the combustor, or exhaust temperature of the gas turbine, or combination of any two or more temperatures thereof, and abnormality is taken by at least one of an absolute value, variation range and change rate of the quantity of state, or combination of any two or more values thereof.
Further, the expected object is attained in the control method of a gas turbine in which in the case where during continuous operation at a prescribed partial load to which the load is lowered, the above-mentioned quantity of state is monitored and comes within an allowable value, or further, in the case where a prescribed time has passed, the combustion condition is regarded as being freed from the abnormal condition and a control quantity is automatically restored to a set value before occurrence of the abnormal condition.